1. Field of the Invention
The invention relates generally to vane pumps and more specifically to a balanced vane pump for automotive power steering systems having a three lobe cam ring and three pairs of inlet and outlet ports.
2. Description of Related Art
Vane pumps typically used in vehicular power steering systems in automobiles, sport utility vehicles, pickup trucks and the like represent a significant source of noise because they provide a pulsatile output. Such a rippling or pulsing output interacts with the hydraulic circuit to create harmonic pressure pulsations which may be characterized as fluid borne noise. Currently utilized balanced vane pumps have two inlet ports and two outlet ports disposed in diametrically opposed pairs. So configured, a completely hydraulically balanced device is achieved. That is, for every force and compressive action occurring at one specific circumferential location or vane on the rotor, the same force or action is occurring at a diametrically opposed location. Generally speaking therefore, the forces in the pump and particularly those against the rotor and vanes relative to the axis of rotation of the rotor cancel each other.
A conventional power steering pump has ten vanes and a rotor which rotates within a cam ring having two oppositely disposed lobes. A pumping region or volume is formed between any two adjacent vanes twice in each revolution, which allows each pumping volume to pump twice per revolution. There are, thus, twenty flow pulses generated per revolution, which represent potential sources of noise.
With increased emphasis on reducing noise, vibration and harshness (NVH) in motor vehicles, all operating systems and components have come under scrutiny. Components of power steering systems which are typically hydraulic and energized by a rotary vane pump have been included in such examination. The present invention relates to such a device.
A balanced rotary vane pump for a motor vehicle power steering system includes a rotor having fifteen vanes disposed in a three lobe cam ring. Three inlet ports and three outlet ports disposed in equally spaced pairs provide fluid communication to the three lobes of the cam ring. Because the subject vane pump provides a significantly larger number of pump pulses per revolution which are more closely spaced in time and may define smaller volumes, the pulsatile nature of the output and thus vibration as well as the excitation of sympathetic vibration is greatly reduced.
It is thus an object of the present invention to provide a rotary vane pump having three equally spaced pumping lobes in a cam ring and three pairs of inlet and outlet ports.
It is a further object of the present invention to provide a rotary vane pump for vehicular power steering systems having reduced noise output.
It is a still further object of the present invention to provide a balanced rotary vane pump having fifteen vanes disposed in a three lobe cam ring.
It is a still further object of the present invention to provide a rotary vane pump for motor vehicle power steering systems which provides a higher number of pumping pulses per revolution of the rotor than currently available units, thus reducing noise generation.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same component, element or feature.